Generally, a vehicular air conditioning system controls a flow direction of conditioned air through a flow passage inside the system, a flow rate of the conditioned air to supply the conditioned air at different temperatures to a plurality of regions of a vehicle interior such that the atmospheric temperatures of the respective regions may be individually controlled. The damper which is opened and closed to control the cross-section area of the flow passage has been employed for controlling the flow direction and the flow rate of the conditioned air.
Under the control of the flow direction or flow rate of the conditioned air using the damper as described above, it is well known that the abnormal noise (air noise or wind noise; hereinafter referred to as the air noise) is heard when the conditioned air passes the region with the reduced cross-section area, that is, the small opening of the damper as described below. Various techniques have been proposed to prevent or suppress generation of the aforementioned air noise (for example, in Patent Documents 1 to 3).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-69489
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2005-205990
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2006-182245